Polymer dispersed liquid crystal (PDLC) may be used for forming a liquid crystal layer of a Liquid Crystal Display (LCD) to serve as a display medium. The PDLC has the characteristics of controlling light transmission by light scattering intensity without employing a polarizing plate. Generally, the PDLC comprises liquid crystal molecules and a polymer matrix. The optical characteristics of the PDLC layer mainly depend on an effective refractive index of the liquid crystal molecules and a matching degree of the liquid crystal molecules with the polymer matrix.
An ordinary PDLC layer is generally fabricated with a positive liquid crystal. When no voltage is applied, the liquid crystal molecules in the ordinary PDLC layer are in a random state, light is refracted and reflected for many times on the interface of the liquid crystal molecules and the polymer matrix after it enters into the ordinary PDLC layer, and in this case, the ordinary PDLC layer presents a milky scattering state. When a voltage is applied, the liquid crystal molecules in the ordinary PDLC layer are arranged along the direction of the electric field, the light is not refracted or reflected after it enters into the ordinary PDLC layer, and in this case, the light is transmitted directly.
A trans-PDLC layer is generally fabricated with a negative liquid crystal. When no voltage is applied, the liquid crystal molecules in the trans-PDLC layer are arranged perpendicular to a substrate of the liquid crystal display, and the light is not refracted or reflected after it enters into the trans-PDLC layer, and in this case, the light is transmitted directly. When a voltage is applied, the liquid crystal molecules in the trans-PDLC layer are arranged in a direction perpendicular to the electric field, the light is refracted and reflected for many times on the interface of the liquid crystal molecules and the polymer matrix after it enters into the trans-PDLC layer, and in this case, the trans-PDLC layer presents the milky scattering state.
The characteristics of the liquid crystal molecules per se have a great influence on the optical properties of the PDLC layer. Due to a certain defect of the physical property of the negative liquid crystal, the trans-PDLC layer fabricated with the negative liquid crystal possesses the disadvantages of high driving voltage, low contrast ratio and the like.